Electronic postage meter systems have been developed, as for example, the systems disclosed in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM, and in European Patent Application, Application No. 80400603.9, filed May 5, 1980 for ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES. Electronic postage meters have also been developed employing plural computing systems. Such a system is shown in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS.
The accounting circuits of electronic postage meters include non-volatile memory capability to store postage accounting information. This information may include the amount of postage remaining in the meter for subsequent printing or the total amount of postage printed by the meter. Other types of accounting or operating data may also be stored in the non-volatile memory. The non-volatile memory function in the electronic accounting circuits have replaced the function served in previous mechanical type postage meters by mechanical accounting registers. Postage meters with mechanical accounting registers are not subject to many problems encountered by electronic postage meters. Conditions cannot normally occur in mechanical type postage meters that prevent the accounting for a printing cycle or which result in the loss of data stored in the registers.
Conditions can occur in electronic postage meters where information stored in electronic accounting circuits can be permanently lost. Conditions such as a total power failure or fluctuation in voltage can cause the microprocessor associated with the meter to operate erratically and either cause a loss of data or the storage of spurious data in the non-volatile memory. The loss of data or the storage of spurious data may result in the loss of information representing the postage funds stored in the meter. Since data of this type changes with the printing of postage and is not stored elsewhere outside of the meter, there is no way to recover or reconstruct the lost information. In such a situation, a user may suffer a loss of postage funds.
To minimize the likelihood of a loss of information stored in the electronic accounting circuits, efforts have been expended to insure the high reliability of electronic postage meters. Some systems for protecting the critical information stored in meters are disclosed in the above-noted patents as well as in U.S. Pat. No. 4,285,050 for ELECTRONIC POSTAGE METER OPERATING VOLTAGE VARIATION SENSING SYSTEM and in U.S. patent application Ser. No. 306,979 filed Oct. 5, 1981, for MEMORY PROTECTION CIRCUIT FOR AN ELECTRONIC POSTAGE METER, and assigned to Pitney Bowes Inc. These systems provide protection against unpredictable circuit operation even if the microprocessor manfunctions at low voltage levels, as for example, where the microprocessor turns off below a predetermined voltage level and thereafter, within a lower voltage range, turns on again and becomes capable of outputting data.